Public Research Seminar by Advanced Materials Thrust, Function Hub,HKUST(GZ) - Thermoelectric Materials: A bird’s eye view from Transmission Electron Microscopy and Beyond
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Transmission electron microscopy is a most powerful technique for characterizing the microstructure and fine atomic structures of materials, especially with the introduction of aberration correction. In this presentation, I will focus on thermoelectric materials, and give a talk about our recent work on revealing the structure-property relationships in materials with ferroelectric properties, such as GeTe, and materials with liquid-like properties, such as AgCrSe2, using TEM and theoretical calculations.
In the GeTe system, we systematically studied the atomic structure and local electrical potential of the van der Waals gap-like defects in a combination of in situ characterization, atomic resolution STEM HAADF, differential phase contrast imaging and electron holography. With the aid of theoretical calculations, it was further demonstrated that the atomic-scale potential wells generated by these layered defects can effectively scatter phonons, while allowing good charge carrier transmission; thus giving rise to the charge carrier-phonon decoupling and good thermoelectric performance.
In the AgCrSe2 system, we characterized the dynamic "hopping" migration mechanism of diffusing Ag ions using in situ atomic resolution STEM HAADF and ab initio molecular dynamics simulations. We found that the typical migration time of Ag ions is longer than the characteristic time of their phonon vibrations, and proposed an ion migration-phonon decoupling model to explain the origin of the ultra-low lattice thermal conductivity. Furthermore, we studied the anharmonic lattice dynamics of AgCrSe2 using many-body perturbation theory, and discovered strong four-phonon resonant scattering in the ordered phase of AgCrSe2, which qualitatively explains the anomalous low-temperature thermal conductivity behavior of AgCrSe2.
Lin Xie is a research associate professor at the Department of Physics, Southern University of Science and Technology. He graduated from the Department of Materials Science and Engineering at Tsinghua University with a bachelor's degree in 2007 and received his Ph.D. in Materials Science and Engineering from Tsinghua University in 2012, where he was supervised by Professor Jing Zhu, an expert in the field of electron microscopy in China. In recent years, his research interests and areas of expertise have focused mainly on studying electron-phonon coupling, spontaneous symmetry breaking and structural distortion, anharmonic lattice dynamics and thermal transport in functional materials such as ferroelectric and thermoelectric materials, using advanced transmission electron microscopy, DFT calculations, and many-body perturbation theories. He has published more than 30 articles in Physical Review Letters, Advanced Materials, Nature Communications, and Angewandte Chemie in the past five years as the first author and corresponding author.